Current-interrupter for electric circuits



C. E. BENNETT.

CURRENT INTERRUPTER FOR ELECTRIC CIRCUITS.

APPUCATION FILED MAY 19, 1919.

1 $359,222. Patented Nov. 16,1920.

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CURRENT INTEHRUPTER FOR ELECTRHJ CIRCUITS.

APPLICATION FILED MAY19| I919.

Patented Nov. 16, 1920.

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tain'ed b UNITED PATENT OFFICE.

CHARLES E..BENNETT, OF ATLANTA. GEORGIA, ASSIGNOR OF ONE-HALF TO MAR-SHALL P. MAXWELL; O1

ATLANTA, GEORGIA.

- CUERENT-INTERBUPTER FOR ELECTRIC CIRCUITS.

Specification of Letters latent.

Patented Nov. 16, 1920.

Application filed May 19, 1919. Serial No. 298,273.

To (LU whom it may concern Be it known that l, UHAnLns E. BENNETT, acitizen of the United States of America, residing in the. city ofAtlanta, county oi Fulton, andSt-ate of Georgia, have invented a.certain new and useful improvement in Current-Internlpters for Electric(in-nits. of which the following is a specification.

My invention relates to current interruir ters for electric circuits.and particularly to a. high-spced-gap device applicable to theprotection of electrical apparatus from injury due either to line surges(:r to high treqnency current imposed thereon.

In the acconr ranying drawings- Figures 1 and 2 are diagrammatic represent-ations of installations in which my invention is embodied indifferent forms.

In the form shown in Fig. 1 the transformer or other equipment 5 to beprotected is connected through a choke coil or inductance 6 to the line7. Shunted around this coil and in multiple with it is a small gap 8 anda. condenser 9 in series therewith on the equipment side of the gap. Aground line 10 is connected to the terminal 11,here shown as a sphere,spaced from the gap horns-12 and 13 predetermined distances. usuallyunequal, dependent upon the volt age of the line 7. The spacing betweenthe horns at the gap 8 is very slight, say to s an inch, and thespi cingbetween the horn 12 and the ground terminal 11 is less than the spacingbetween the horn 13 and the terminal 11. A current breaker 14 arrangedin the ground line 10 may be of any suitable construction.

If a surge or over-voltage occurs on the line 7 at normal low frequencyan are forms at once between the horn 13 and the terminal 11, and thecurrent discharged through the ground line 10 and quickly broken at 14.

Should a transient high frequency po' tential, even of low voltage, beimposed upon the line, the choke coil 6 prevents its flow to thetransformer 5, and builds up a local high potential in the circuitthrough the coil 6, condenser 9 and gap 8, with the result that thecurrent arcs across gap 8. The are thus formed at the gap 8 is mainthenormal line current, and rising in t e horns 12 and 13 breaks thedielectric strength of the air adjacent the sphere 11, jumps from horn12 to terminal.

11, and the current passes from horn 13 to the ground. line 10, where itbroken at 1 1.

Should the frequency of the transient potential be extremely high thecurrent .will build up a very high potential on a few end turns of thecoil (5, thereby inducing in the remaining turns a still higher potential which tends to form an zu'cncross the gap 8 through the condenser9.

At normal frequency the condenser 9 is of high impedance between lhcpoint 15 and the horn 12. This make. it possibie' .to set the hornsclose together so that the gap 8 may be very small without danger of apotential flow or arc-over between the horns. In the event of a currentof high frequency imposed upon the line, however, the current. passesthe condenser and arcs the gap This lowers the potential at the horn 12to a. voltage corresponding to that of the ground line 10, which isdetermined by that of the automatic circuit breaker 14. Inasmuch as thegap 8 is very small as compared to that between the horn 13 and groundterminal 11, an arc is established at 8 followed immediately by its riseand jump from the horn 12 to the ground terminal 11, the discharge overthe ground line 10 being shortly broken at 14.

The particular construction of the apparatus arranged in accordance withthe diagram is of no particular moment. Thus the terminals of the horns12 and 13 may be spherical, hemi spherical or pointed, as may prove mostadvantageous. Similarly the terminals at the ga 8 may be hemi-sphcricalor otherwise. he constructions of the condenser 9 and of the choke coil6 possess no unusual features.

The arrangement indicated in Fig. 2 involves the same generalprinciples, but affords a still reater safe-guard for the equipment 5.he connection to the equipment is here made from the choke coil 6 at apoint 16 midway between the ends of its turns. At one end the coil isconnected to the line 7. Shuntcd around this coil is the'gap 8 in serieswith a condenser 9 connectedat 17 to the opposite end of the choke coil6. From a point intermediate the condenser 9 and thegap is a lead 18,which is carried through a main condenser 19 to the ground line 10 atthe point 20 above the automatic circuit breaker 14.

With this arrangement the operation is as follows: When a high frequencycurrent is imposed on the line 7 it attempts to pass through the coil 6to the transformer 5, but is choked by the coil and builds up a magneticflux which induces a higher voltage in all of the turnsan autotransformer efiect similar to that occurring in the construction firstdescribed. This builds up a local high potential in the circuit throughthe coil 6, condenser 9, gap 8, and back to line 7. As the gap 8 is veryshort, approximately a to 1} of an inch, the induced high potentialcurrent arcs this gap and the high frequency current on the line nowflows across the gap and through the main condenser 19 to ground line10. Inasmuch as the condenser 19 is of such construction that it willallow the normal current of the power line to flow therethrough, thiscurrent maintains the arc established by the momentary high, frequencycurrent and the hot arc which results rises on horns 13-12 until it istransferred to the terminal 11, whereupon the current passes directlyinto the ground line 10 ani is broken at the interrupter 14, thusreestablishing normal conditions on the line.

The main condenser 19 is so constructed that the voltage drop thereoveris such that the gap 8 may be made extremely short since at lowfrequency of the line the potential difference between the horns 12 and13 will not be sufficient to cause an arc to form.

In addition to the features above referred to it should be borne in mindthat the gap between the horns l2 and 13 and between the horns in theground terminal 11, as well as the condensers 9 and 19 may be soadjusted that the device will respond with accuracy to any frequencynear the natural period of the transformer or other equipment pro tectedby this high speed gap. In other words, every transformer, or the like,has some relative ratio of capacity to its indu tance and the naturalperiod is the point at which these two are'equal, so that resonanceoccurs. Any of the harmonics of this natural period become damaging tothe equipment. Therefore, if the high speed gap be so constructed andarranged that the inductance of the choke coil and auxiliary condensersrespond to'any given setting, practically absolute protection of theequipment is secured. This functioning is similar to that of the tuningup of a wireless outfit, the capacity remaining constant but varying theindu'tame until resonance is secured. The present apparatus possessesthe highlydesi able characteristics that its gaps may be set selectivelywith relation to anormal line current, and the resonance of theequipment which it is designed to protect, and will operate todisahargethe line of any overvoltage or high frequency current imposedthereon at any predetermined frequency or harmonics that may endangerthe equip ment.

The arrester 14 may be of any suitable construction, such for instanceas that dis 7 sociated with but spaced from the gap terminals, anautomatic current interrupter in the ground connection, a ca acity inseries with the gap in the linegan an inductancc lay-passing the gap andcondenser in the line.

2. An electric circuit having therein a horn gap, :1 ground connectionterminal associated with but spaced unequal distances from the gapterminals, an automatic current interrupter in the ground connection, acapacity in series with the gap in the line and an inductance by-passingthe gap and condenser in the line.

3. An electric circuit having therein a horn gap, at ground connectionterminatessociated with but spaced from the ap terminals and arrangedcloser to the horn on the. condenser side of the gap, an automaticcurrent interrupter in the ground connection, a capacity in series withthe gap in the line and an inductance by-pas'sing the gap and condenserin the line.

4. An electric circuit having therein a horn gap, a ground connectionterminal associated with but spaced from the gap terminals, an automaticcurrent interrupter in the ground connection, a capacity in series withthe gap in the line, and an inductance by-passing the gap and condenserin the line, together with a capacity by-passing the ground terminal atthe gap and connecting the ground line to the power line between the gapand the capacity in the line.

5. An electric circuit having therein a horn gap, a ground connectionterminal associated with but spaced from the gap terminals, an automaticcurrent interrupter in the ground connection, a ca acity in series withthe gap in the line, and an inductance lay-passing the gap andcon-denser in the line, the line connection being madet'o the inductanceintermediate the ends of the coil-.

In testimony whereof I have signed my name to this specification.

CHARLES E. BENNETT.

